Emulsions that have been homogenized are known in the art. They typically require stabilizing gums or thickeners to maintain the stability of the discrete oil phase within the continuous water phase. The type and concentration of emulsifiers, as well as the viscosity of the emulsion, influence the overall stability of the emulsion. Standard propeller-type mixers or standard homogenizers are typically used to manufacture emulsions.
Emulsions made by high pressure homogenization are also known. These emulsions can range from thick, non-flowing creams to light lotions. The light lotions typically require a post addition after high pressure homogenization of a gum or thickener to stabilize the emulsion.
U.S. Pat. No. 4,996,004 to Bucheler et al. provides, in its discussion of the prior art, the formation of cosmetic emulsions by combining heated oily and aqueous phases, cooling the mixture and dispersing it in a "high-pressure" homogenizer at levels of about 200 bar [col. 1, lines 19-44]. However, no suggestion is made that thickeners or gums can be eliminated, or that lower levels of emulsifiers are effective.
U.S. Pat. No. 5,152,923 to Weder et al. provides a process for producing a stable nanoemulsion of oil particles, specifically triglyceride or fatty acid esters, in a water phase using 0.1 to 0.4 parts by weight of a lecithin-type amphoteric emulsifier. The emulsifier forms a lamellar liquid-crystalline structure in the aqueous phase. The mixture is then processed into a nanoemulsion in a high-pressure homogenizer, at pressures of 500 to 1000 bar. Moreover, tests have shown that emulsions formed with the emulsifiers taught by this patent are viscous, and are unstable at elevated temperatures.